In a background art, in some image forming apparatus, a photoreceptor drum or photoreceptor belt (hereinafter referred to as a photoreceptor) constituting an electrostatic latent image carrier is rotatably supported on a main body of the image forming apparatus, an electrostatic latent image is formed on a light-sensitive layer of the photoreceptor at the time of image formation operation, thereafter, the latent image is visualized with a developing agent of a developing device, and then, the visible image is transferred onto a recording material by using a corona transfer unit, transfer roller, transfer drum or transfer belt (hereinafter referred to as a transfer medium). Also, in some full-color image forming apparatus, a tandem apparatus, a system in which a plurality of color images are sequentially transferred onto the recording material such as a paper on the transfer belt or transfer drum, one over the other, using a plurality of photoreceptors or a plurality of developing mechanisms, and then fixed, is used. Further, in some image forming apparatus, an apparatus of a 4-cycle intermediate transfer system in which color images are sequentially primarily transferred onto an intermediate transfer medium to perform color superposition, and the primarily transferred images are secondarily transferred together to a transfer material, and an apparatus of a rotary developing system are used.
Further, a developing device having a primary reservoir, a secondary reservoir and a stirring member in order to use a developing agent in cycles is used. For example, in reference 1 and reference 2, a toner-circulating developing device in which a non-magnetic mono-component toner, a developing agent, is supplied to a developing member by a supply member through a regulating member to allow a thin layer of the toner to be kept on the developing member, wherein the toner which has not been fed onto the developing member through regulation by the regulating member is allowed to fall down, stirred together with the already existing toner in the primary reservoir, and then, transferred to the secondary reservoir.
Furthermore, for example, in references 3 to 6, plural kinds of external additives different in primary particle size are added to a toner in order to obtain stable print quality for a long period of time in continuous printing, and further, that an abrasive having a large particle size is added to prevent filming on a photoreceptor, an electrostatic latent image carrier.
[Reference 1] JP2001-42614 A
[Reference 2] JP2003-173081 A
[Reference 3] JP63-289559 A
[Reference 4] JP2001-147547 A
[Reference 5] JP11-184144 A
[Reference 6] JP2003-322998 A
However, in the developing device as shown in reference 1 and reference 2, when a used developing cartridge is recycled to use, fine particles which are an external additive of a toner firmly adhere to a stirring member in the developing device, and it is almost impossible to remove the particles even when air is blasted for cleaning, which has caused the problem of taking a long time to clean the cartridge to reduce the production efficiency in a recycling process.
Further, also in the case of references 3 to 6, when an external additive is added to a toner in an amount of 2% by weight or more, the external additive is liberated from a surface of the toner, and the liberated external additive adheres to portions with which the toner is in contact in a developing cartridge, which has caused a factor contributing to taking a long time to clean the cartridge to reduce the production efficiency in recycling the used cartridge.